The present invention is directed to an add drop apparatus and method of using the same in wave division multiplexed (WDM) systems and more particularly to a method and apparatus of novel design for dispersion compensation and adding/dropping select signals.
Dispersion of light is a well-known natural phenomenon. It is well known that dispersion is problematic in the optical transmission arts. A standard single mode fiber, commonly used in optical transmission systems, has a wavelength of about 1550 nm and a group velocity dispersion of about 17 ps(nm-km) . The dispersion causes high bit rate transmissions and transmissions over long distances to be distorted and become potentially indecipherable at the receiving ends. A second source of dispersion in fibers is non-linearities in the fiber whose destructive effects are brought about by the use of high optical transmission power required for transmission along longer transmission lines.
In the past, many solutions have been proposed to dispersion along long transmission lines. Use of dispersion compensation fiber modules are well known in the art. Such modules include several kilometers of wound optical fiber, the fiber normally having a negative dispersion of about 100 ps(nm-km). Judiciously applied throughout a transmission system, the fiber modules can compensate exactly the dispersion of a certain wavelength if the spread of the signal in the fiber is not influenced additionally by non-linear effects.